Tunning
Thread Starter
Drifting
Joined: Jan 2018
Posts: 1,255
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From: Western NY
Tunning
I am looking to tune the L-79 on my 66 Vert as per Lars tech articles on Ignition first, followed by the Holley. Up first I need to confirm top dead center on the balancer OE mark and the pointer. Lars has a article on this procedure but I have not been able to locate it here on the forum. I am thinking:
Disconnect battery
Pull the plugs
Place a section of blunt piano wire in #1 spark plug hole.
Rotate motor at the balancer nut until the wire moves as far out of the hole as it can
Visually check the timing mark on the balancer relative to the pointer
Adjust the pointer if necessary
That sound correct? Is it safe to assume the balancer nut IS NOT reverse thread so righty tighty applies?
Thanks Guys
Disconnect battery
Pull the plugs
Place a section of blunt piano wire in #1 spark plug hole.
Rotate motor at the balancer nut until the wire moves as far out of the hole as it can
Visually check the timing mark on the balancer relative to the pointer
Adjust the pointer if necessary
That sound correct? Is it safe to assume the balancer nut IS NOT reverse thread so righty tighty applies?
Thanks Guys
Drifting
Joined: Apr 2017
Posts: 1,377
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From: Bedford New York
On the #1 cylinder, make sure the intake and the exhaust valves are both CLOSED while the #1 piston is up at it's highest position. You want to be on the compression cycle for TDC.
Last edited by Tonio; Jul 31, 2019 at 01:00 PM.
Race Director
Joined: Apr 2005
Posts: 11,265
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From: Bowling Green, Kentucky
I think there are better ways to get TDC accurately. There is quite a range of degrees when piston is at or near TDC and exhibits very little movement. A piston stop and a degree wheel are more accurate.
For original C2 balancers, TDC mark is aligned with the balancer keyway. This changed for later years. I guess degree scale on timing chain cover could also be different location from original.........so best to use piston stop and degree wheel for 100% proof.
Larry
PS: Email Lars and he will send you his tech article. His email address is in the archives.......or someone will post.
For original C2 balancers, TDC mark is aligned with the balancer keyway. This changed for later years. I guess degree scale on timing chain cover could also be different location from original.........so best to use piston stop and degree wheel for 100% proof.
Larry
PS: Email Lars and he will send you his tech article. His email address is in the archives.......or someone will post.
Last edited by Powershift; Jul 31, 2019 at 01:12 PM.
Thread Starter
Drifting
Joined: Jan 2018
Posts: 1,255
Likes: 316
From: Western NY
So to confirm the compression stroke, I should feel air escaping from the spark plug hole...yes?
As for a piston stop, I have to look into that, never heard of it (novice wrench turner).
I did email Lars yesterday, no joy so far. He's a busy dude, maybe in the next few days. Car runs fine now so there is no hurry, just like the ides of setting her up as correctly as my skill sets, or lack there of, will allow.
Here is another question. I pulled the distributor cap (I have the SE ignition) and took a look at the VAC. Lars and Duke seem to talk about the B26 and B20 (VN1765) as the unit of choice for the L-79. The unit I have is a MS 236 16 (which I am not seeing on a Google search). The 16 indicates the 16* of advance when she is full in and that is the same as the rating on the two units Duke/Lars reference so I am assuming that's good. You guy's agree??
As for a piston stop, I have to look into that, never heard of it (novice wrench turner).
I did email Lars yesterday, no joy so far. He's a busy dude, maybe in the next few days. Car runs fine now so there is no hurry, just like the ides of setting her up as correctly as my skill sets, or lack there of, will allow.
Here is another question. I pulled the distributor cap (I have the SE ignition) and took a look at the VAC. Lars and Duke seem to talk about the B26 and B20 (VN1765) as the unit of choice for the L-79. The unit I have is a MS 236 16 (which I am not seeing on a Google search). The 16 indicates the 16* of advance when she is full in and that is the same as the rating on the two units Duke/Lars reference so I am assuming that's good. You guy's agree??
Le Mans Master
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From: Pittsburgh
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Actually, I use a whistle made to be inserted in the #1 spark plug hole.........Works extremely well to find TDC references.
Race Director
Joined: Apr 2005
Posts: 11,265
Likes: 2,131
From: Bowling Green, Kentucky
So to confirm the compression stroke, I should feel air escaping from the spark plug hole...yes?
As for a piston stop, I have to look into that, never heard of it (novice wrench turner).
I did email Lars yesterday, no joy so far. He's a busy dude, maybe in the next few days. Car runs fine now so there is no hurry, just like the ides of setting her up as correctly as my skill sets, or lack there of, will allow.
Here is another question. I pulled the distributor cap (I have the SE ignition) and took a look at the VAC. Lars and Duke seem to talk about the B26 and B20 (VN1765) as the unit of choice for the L-79. The unit I have is a MS 236 16 (which I am not seeing on a Google search). The 16 indicates the 16* of advance when she is full in and that is the same as the rating on the two units Duke/Lars reference so I am assuming that's good. You guy's agree??
As for a piston stop, I have to look into that, never heard of it (novice wrench turner).
I did email Lars yesterday, no joy so far. He's a busy dude, maybe in the next few days. Car runs fine now so there is no hurry, just like the ides of setting her up as correctly as my skill sets, or lack there of, will allow.
Here is another question. I pulled the distributor cap (I have the SE ignition) and took a look at the VAC. Lars and Duke seem to talk about the B26 and B20 (VN1765) as the unit of choice for the L-79. The unit I have is a MS 236 16 (which I am not seeing on a Google search). The 16 indicates the 16* of advance when she is full in and that is the same as the rating on the two units Duke/Lars reference so I am assuming that's good. You guy's agree??
Jegs and Summit and others have the piston stop. You can also make one. It is most accurate, and the way the engine builders determine TDC. Also quite cheap to buy.
Yes, air escaping from cylinder is piston moving up to TDC. But you can also look at the valves/rockers and also at the distributor rotor tip to determine this.
Larry
EDIT: Here is one from Summit. A bit on the cheap side, but should work just fine. There are better ones if you check. https://www.summitracing.com/parts/cca-4795?rrec=true
Last edited by Powershift; Jul 31, 2019 at 02:56 PM.
Safety Car
Joined: Mar 2009
Posts: 4,191
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From: Corpus Christi, TX
If all you need is confirmation of the timing mark on the balancer and the pointer location, it doesn't matter whether you're on #1 firing or #6, which is one full crank rotation out from #1. If you're degreeing the can or setting up the distributor, that's another matter.
Race Director
Joined: Apr 2005
Posts: 11,265
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From: Bowling Green, Kentucky
If all you need is confirmation of the timing mark on the balancer and the pointer location, it doesn't matter whether you're on #1 firing or #6, which is one full crank rotation out from #1. If you're degreeing the can or setting up the distributor, that's another matter.
Agreed. I was just trying to answer his question about TDC. 
But your answer is an even better one for him.........he can't miss. 
Larry
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Thread Starter
Drifting
Joined: Jan 2018
Posts: 1,255
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From: Western NY
OK Larry, I ordered the piston stop and picked up a timing tape for the balancer. I should be able to temporarily attach the tape to the balancer and using your stop, spin it both ways, do the math and find TDC. I could then either adjust the pointer or mark the balancer for future reference. I like the idea of using the rotor to determine compression stroke over visualizing the valves, just replaced both gaskets and would like not to disturb them. So if I wrench the motor over until the rotor is pointing at the #1 plug wire position (with air escaping from the plug hole), I'm on the compression stroke?
Thanks for the schooling.
Thanks for the schooling.
Safety Car
Joined: Mar 2009
Posts: 4,191
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From: Corpus Christi, TX
Yes, rotor pointing at #1 and at TDC, you're at the end of compression on #1. The valve check is goid if you pulled the distributor and don't know whether you're on 1 or 6.
Extra bonus question, if you have the timing chain cover off and the sprocket dots are opposite each other, you're on #6.
Extra bonus question, if you have the timing chain cover off and the sprocket dots are opposite each other, you're on #6.
Last edited by Avispa; Jul 31, 2019 at 04:10 PM.
Thread Starter
Drifting
Joined: Jan 2018
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From: Western NY
Sorry I missed Avispa's post. So your saying that I can use the piston stop on any cylinder because when any cylinder is at TDC, the pointer should be aligned with the balancer mark?
Safety Car
Joined: Mar 2009
Posts: 4,191
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From: Corpus Christi, TX
NO!!! TDC on the pointer is TDC ONLY on 1 and 6!!!! Sorry for the shout. I don't wanna make somebody blow up his motor.
Last edited by Avispa; Jul 31, 2019 at 04:12 PM.
Race Director
Joined: Apr 2005
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From: Bowling Green, Kentucky
2. Not much math involved. Mark where #1 piston stops. Rotate engine the other direction until it stops. Mark this location or degrees. TDC is exactly 1/2 of the distance or degrees (for the smaller angle) between these two marks.
Larry
Le Mans Master
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I set my timing on my 283, last tuneup, using a Vacuum gauge with .......turning the Electronic ignition distributor for max vacuum then backing it off from High vacuum achieved by 1* of vacuum to reduce "ping"...........No timing light used.......I used this method when I burned up my Digital Timing Light Harness on my header..............
Race Director
Joined: Apr 2005
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From: Bowling Green, Kentucky
I set my timing on my 283, last tuneup, using a Vacuum gauge with .......turning the Electronic ignition distributor for max vacuum then backing it off from High vacuum achieved by 1* of vacuum to reduce "ping"...........No timing light used.......I used this method when I burned up my Digital Timing Light Harness on my header..............
Buy yourself a new timing light and use it. 
Vacuum gages have their place in tune-ups and engine diagnostics, but setting and checking timing with SHP engines and today's gas isn't it.
Larry
Race Director
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Here is another question. I pulled the distributor cap (I have the SE ignition) and took a look at the VAC. Lars and Duke seem to talk about the B26 and B20 (VN1765) as the unit of choice for the L-79. The unit I have is a MS 236 16 (which I am not seeing on a Google search). The 16 indicates the 16* of advance when she is full in and that is the same as the rating on the two units Duke/Lars reference so I am assuming that's good. You guy's agree??
Information I received since I wrote that article indicates that the black springs in the Mr. Gasket 928G spring kit are the lightest and gold the heaviest.
Since it will also be on the page of threads started by me, read the tuning seminar, too.
Duke
Thread Starter
Drifting
Joined: Jan 2018
Posts: 1,255
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From: Western NY
Hi Duke,
At the moment I am working off of:
Lars-Distributor Vacuum Advance Control Units Specs and Facts for GM Distributors (Rev-9-2-18)
- How to set your timing for peak performance (Rev. 4-2-18)
Duke- Vacuum advance principals and applications
Hinckley- Timing and Vacuum Advance 101
- Advanced Curves, fine tuning your Corvettes distributor
Thankfully there appears to be some overlap of opinion among the 3 of you. I will search and read the additional works you referenced prior to initiating the project. Ordered a piston stop and a timing tape, probably be next week before any of that arrives.
Thank you sir.
At the moment I am working off of:
Lars-Distributor Vacuum Advance Control Units Specs and Facts for GM Distributors (Rev-9-2-18)
- How to set your timing for peak performance (Rev. 4-2-18)
Duke- Vacuum advance principals and applications
Hinckley- Timing and Vacuum Advance 101
- Advanced Curves, fine tuning your Corvettes distributor
Thankfully there appears to be some overlap of opinion among the 3 of you. I will search and read the additional works you referenced prior to initiating the project. Ordered a piston stop and a timing tape, probably be next week before any of that arrives.
Thank you sir.
Thread Starter
Drifting
Joined: Jan 2018
Posts: 1,255
Likes: 316
From: Western NY
I did also order the Mr. Gasket 928G kit, awaiting that as well. My plan today was to use a Mighty-Vac to confirm my OE VAC works, at what vac it begins to move and at what vac it maxes out at. Sounds like you support replacing it with the B26 so I'll read your work on that and source one. Guess I'll preserve the OE unit for the next owner (once I assume room temperature that is)
Team Owner
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Army
"Advancing just before engine kickback" and "timing with a vacuum gauge" will get you running and close to initial timing in many cases. It does nothing for your advance map or optimization for a specific engine..